To supply compressed air to pneumatic consumers such as compressed-air brakes of motor vehicles, compressed air supply devices are known, in which the compressor compresses intake air and supplies the air via a pressure line to a storage vessel, and from which the air is extracted as required. In motor vehicle applications, the humidity of the compressed air is undesirable. DE 10 2006 035 772 A1 discloses a compressed air processing device for motor vehicles, in which a dehumidification device is provided in the pressure line such that the compressed air is dried before entering the storage vessel.
The compressed air is however also often contaminated with damaging matter from the intake air and with oil products and oil decomposition products from the compression process of the compressor, which is usually lubricated with oil. These contaminants—which are present in the compressed air in addition to the water—will for simplicity hereinafter be referred to as oil products. A large proportion of the oil products is present as aerosol, which moves with the compressed air and can therefore pass into the entire compressed air system. There, the oil products can lead to damage, for example as a result of the swelling, sticking or decomposition of seal elements. To protect the compressed air device, and the compressed air units connected thereto, against contamination with oil products, the compressed air in the pressure line is generally purified of oil products.
Here, solutions for the processing of the compressed air have already been proposed in which the purification of the oil takes place before the drying. Here, it is known for a separate filter, for example a coalescence filter or an oil separator, to be provided as a device for oil purification. However, it has proven to be disadvantageous that separated oil products can be vented into the environment. Oil separators operating according to the cyclone principle separate only aerosols of a particular size and therefore, in many applications, do not permit adequate purification performance. In particular, however, the filtering of the compressed air before it flows through the dryer has the effect that the device for oil purification is impinged on both with oil products and also with water. The filter element therefore separates a considerable amount of liquid as a mixture of oil and water, which must be disposed of in considerable quantities, which in turn necessitates frequent servicing of the filter, and under some circumstances impairs the function thereof.
It has also already been proposed that the oil purification first be carried out downstream of the drying agent. DE 103 135 75 A1 discloses a cartridge device for an air dryer, in which the means for removing damaging chemical compounds, in particular hydrocarbon compounds, is positioned downstream of the drying agent with respect to the flow direction of the air. The fact that filtration first takes place downstream of the drying agent, however, often leads to excessive contamination of the drying agent, which significantly reduces the drying performance.